Technical parameters of a conventional class-D audio power amplifier circuit tend to be designed to fixed parameters, for example, fixed carrier frequency, fixed frequency response, fixed gain setting (when stably-working), fixed temperature protection point, fixed driver current, and the like. Such design is simple. However, a drawback of such design lies in that when peripheral conditions of the circuit change or internal conditions thereof change, adjustment fails to be made to accommodate to these changes. Therefore, the best performance cannot be reached under different conditions, and under some circumstances, some negative effects may be caused.
For example, when the working temperature of the circuit is ever increasing due to transient changes of the ambient conditions and reaches the temperature protection point, according to the related art, the circuit may temporarily stop working since a temperature protection function which is triggered at a fixed temperature protection point is set. The audience may be unpleasant if no voice is output or even a short interruption of the voice output. Even worse, in most cases, the temperature protection setting of the circuit may repeatedly restart the circuit and thus cause non-contiguous voice output, or may directly cause the circuit to shutdown. In this case, the circuit needs to be restarted.
Still for example, the fixed carrier frequency is generally employed (when the frequency conversion and spectrum spreading technology is applied to reduce EMI) in the related art, which is set to a frequency 10 times higher than the audio domain, with a lower value of 200 kHz and a higher value of 600 kHz. A high-frequency carrier may boost the audio performance, which, compared with a low-frequency carrier, cause notable increase in power consumption and EMI.
Still for example, it is well known that the audio power amplifier circuits are all subject to differences in frequency response performance. Some circuits achieve excellent voice performance within a low-frequency range, some circuits achieve excellent voice performance within a high-frequency range, some circuits achieve excellent low-frequency distortion performance, and some circuits achieve excellent high-frequency distortion performance. When the circuit parameters are fixed, the frequency response is also fixed. Therefore, the employed circuit structure and the manufacture process thereof fail to accommodate frequency responses within various frequency ranges.
Yet still for example, the overshoot phenomenon tends to occur due to the output square wave of the class-D audio power amplifier, thereby causing such problems as distortion, power consumption, and EMI. Such problems are related to the fact that the output stage employs a fixed drive current.
In conclusion, design of fixed parameters in the class-D audio power amplifier circuit in the related art cannot accommodate parameter changes during practical application, and the class-D power amplifier circuit in the related art has defects.